Thank you very much StatDave_sas,    Now I understand that the ONESIDED option affected the p-value, but not the 95% CL, which is one-side even when such an option is not included.    Best regards   Alessandro Mannelli  ... View more

Thank you very much. My problem, however, is that the exact p value is = 0.055 (p>0.05, accept the null hypothesis) whereas the 95% CI lower limit of the odds ratio is 1.24 (being > 1 I would reject the null hypothesis) second, I realise that the ONESIDED option only affects the exact pa value, not the 95% CL's since they are the same as in the two-sided defalt for riskfactor2 Thank you and best regrds ... View more

Good morning, I placed another post with datalines and codes, for the one dataset where I can have data in binomial format (pos / tot), just in case, I paste the same codes here. Sorry in case of double posting!! and thank you very much. I have been a sas user for 30 years but never used this support... data risk; input riskfact1 riskfact2 tot pos; datalines; 0 0 36 0 0 1 93 3 1 0 13 0 1 1 54 11 ; run; proc logistic data=risk exactonly; TITLE ' two-sided '; title2 'Conflicting 95% CLs and exact p-value'; model pos / tot = riskfact1 riskfact2; exact riskfact1 riskfact2 / estimate=both outdist = dist; run; proc logistic data=risk exactonly; TITLE ' one-sided '; title2 ' 95% CLs not affected by onesided option'; model pos / tot = riskfact1 riskfact2; exact riskfact1 riskfact2 / estimate=both outdist = dist onesided; run; ... View more

Good morning.    I used the EXACT  statement in logistic regression to analyse data with quasi complete separation  of results (none of the individuals in the unexposed group was a case). I obtained the median unbiased estimate of the logistic regression parameter. The exact p value was 0.055 but the parameter 95% CL's were 0.18; Infinity. When calculating the odds ratio, the lower limit was greater than 1 (1.24). Furhermore, very disturbingly, after including the ONESIDED option in the EXACT statement, while the p-value was reduce by half, the 95% CL's of the same OR were not changed.  I paste here codes including datalines: 95% CL and exact p value for riskfactor2 are conflicting, furthermore, CL are not affected by onesided option (p-value is)   data risk; input riskfact1 riskfact2 tot pos; datalines; 0 0 36 0 0 1 93 3 1 0 13 0 1 1 54 11 ; run; proc logistic data=risk exactonly; TITLE ' two-sided '; title2 'Conflicting 95% CLs and exact p-value'; model pos / tot = riskfact1 riskfact2; exact riskfact1 riskfact2 / estimate=both outdist = dist; run; proc logistic data=risk exactonly; TITLE ' one-sided '; title2 ' 95% CLs not affected by onesided option'; model pos / tot = riskfact1 riskfact2; exact riskfact1 riskfact2 / estimate=both outdist = dist onesided; run;   Thank you very much for your help    Alessandro Mannelli  ... View more